JP6675068B2 - Blow molding method - Google Patents

Description

  The present invention relates to a blow molding method in which air is blown into a parison sandwiched between molds to perform blow molding, and more particularly to an improvement for making the thickness of a molded product uniform.

  As a method for molding a plastic container (bottle), a blow molding method is widely used. An injection-molded preform is set in a mold, and air is blown into the mold to form a mold cavity. Axial stretch blow molding and the like are known.

  In recent years, in the field of plastic containers, a variety of functions and performances are often required, and contrivance is required for materials to be used and molding methods. For example, when gas barrier properties, light shielding properties, heat retention properties, and the like are required, materials used have gas barrier properties, and colorants and ultraviolet absorbers are added to plastic materials.

  However, there is a limit to the material and the like, and various functions are also provided by forming a plastic container into a multilayer structure. By optimizing the constituent materials and the like of each layer, it is expected that a plastic container having multiple functions such as a light-shielding container having excellent gas barrier properties can be realized.

  In order to mold a multilayer plastic container, it is considered that a multilayer preform may be injection-molded and then blow-molded, and various molding methods of the multilayer preform have been proposed. However, the molding of the multilayer preform requires advanced technology, and there is a problem in terms of cost and the like such that a large amount of equipment investment is required for the molding apparatus.

  Under such circumstances, it has been proposed to attach a separately formed preform cover to the outside of the preform and blow-mold the same to form a composite container (see Patent Documents 1 and 2 and the like). ). By using the preform cover, there is no need to mold a multilayer preform, which is considered to lead to cost reduction and the like.

  Patent Literature 1 discloses that a composite preform having an outer contraction member provided outside a preform, an outer contraction member closely adhered to the outside of the preform, and a preform, is prepared in a blow molding die. A blow molding method in which a preform of a composite preform and an outer contraction member are expanded integrally by performing blow molding on the reform is disclosed. By forming the outer contraction member with a material having, for example, a gas barrier property or a light barrier property, it is possible to mold a composite container provided with these functions.

  Patent Literature 2 discloses a blow molding method in which an inner label member is provided outside a preform and the preform and the inner label member are expanded integrally as in Patent Literature 1. This makes it possible to realize a blow molding method that can eliminate the step of applying a label by a labeler.

JP 2015-9493 A JP-A-2015-9487

  By the way, in a method in which a preform cover is attached to the outside of the preform and the preform cover is blow-molded to form a composite container, it is necessary to form the preform cover in advance according to the shape of the preform. This preform cover may be manufactured by injection molding, but if it can be formed by blow molding, it is expected that the cost can be further reduced.

  However, blow molding has a problem that it is difficult to make the thickness uniform. In the case of blow molding, it is necessary to pinch off both ends of the parison for air blowing, but the parison is easily flattened at the time of this pinch-off, and as a result, the wall thickness is uneven in the circumferential direction. Tends to be.

  In a composite container in which a preform cover is attached to the outside of the above-described preform and blow molded, unevenness in the thickness of the preform cover leads to deterioration in quality, which is not preferable.

  The present invention has been proposed in view of such a conventional situation, and is capable of suppressing uneven thickness in blow molding, and is capable of forming a product having a uniform thickness in a circumferential direction. The aim is to provide a method.

To achieve the foregoing objects, a blow molding method of the present invention is a blow molding method for blow molding is sandwiched by the pair of molds a parison extruded from the extruder, the product to be molded, superimposed preform It is a preform cover to be molded, and the form of the molded body is a form in which a plurality of products are connected, and only the ends of the products at both ends that are not connected are pinched off, and the plurality of products are collectively It is characterized by blow molding.

  In blow molding, the parison is flattened in the vicinity of the pinch-off portion, leading to uneven thickness. Pinching off both ends of one product will spread out areas of non-uniform thickness. In the blow molding method of the present invention, since a plurality of products are collectively molded in a connected form, so-called multiple-piece molding is performed, so that the number of pinch-off portions in each product is reduced, and unevenness in thickness due to pinch-off is reduced. Minimized.

  ADVANTAGE OF THE INVENTION According to the blow molding method of this invention, nonuniformity of thickness can be suppressed and it is possible to shape the product with uniform thickness in the circumferential direction. Therefore, for example, when the preform cover is attached to the outside of the preform and blow molded to produce a composite container, by applying the blow molding method of the present invention to the blow molding of the preform cover, high quality is achieved. It is possible to manufacture a complex container.

It is a schematic side view of a molded object formed in an embodiment. It is a schematic sectional view showing a blow molding method and showing a parison extrusion process. It is a schematic sectional drawing which shows a parison pinching process. It is an outline sectional view showing the state after air blast. It is a longitudinal cross-sectional view which shows typically the form of the parison in one-piece blow molding. It is a cross-sectional view in the XX line of FIG. 3A. It is a longitudinal cross-sectional view which shows typically the form of the parison in two-piece blow molding. It is a cross-sectional view in the YY line of FIG. 3A. FIG. 4 is a schematic perspective view illustrating an example of a manufacturing process of the composite container and illustrating a preform cover mounting process. It is an outline sectional view showing the state where a preform cover was attached to a preform. It is a schematic side view which shows the molded composite container partially broken. It is a figure showing a measurement place which measured thickness distribution in evaluation of an example. It is a figure which shows the thickness distribution of the longitudinal direction of the preform cover shape | molded by the Example.

  Hereinafter, embodiments of a blow molding method to which the present invention is applied will be described with reference to the drawings.

  In the blow molding method of the present invention, in a blow molding method in which a parison extruded from an extruder is sandwiched between a pair of molds and blow molded, a form of a molded body is a form in which a plurality of products are connected, and a product at both ends is connected. Pinch off only the end on the side that is not performed, and blow-mold the plurality of products collectively.

  In other words, in the blow molding method of the present invention, in a so-called multi-cavity state, a plurality of products are connected so as to be connected in series to perform blow molding. The number of products to be collectively molded may be two or three, and may be four or more. However, as the number of products to be molded collectively increases, the size of the mold needs to be increased. . In the case where three or more pieces are molded at a time, the shape of each product is limited to one having both ends opened. Therefore, how many molded bodies are to be molded at once may be appropriately set according to the required product shape, the scale of equipment, and the like.

  Hereinafter, an embodiment of the present invention will be described with an example in which two products are formed collectively. In the case of two pieces, the two products are connected at one end, and only the end of the non-connected side of each product is pinched off to blow-mold the two products at a time. In other words, the parison is sandwiched by the mold only at the end of the product that is not connected, but the parison is not sandwiched by the mold in other portions.

  FIG. 1 shows a form of a molded body 1 molded in the present embodiment. The molded body 1 molded in the present embodiment has a form in which two preform covers (products) 2 and 3 are connected in series. One end of each of the preform covers 2 and 3 is closed as a pinch-off portion 2a, 3a, and the other end is integrally connected to each other via a connecting portion 4 in a state of being opened. .

  The connecting portion 4 for connecting the preform covers 2 and 3 as products is formed with a diameter slightly smaller than the diameter of the body of each of the preform covers 2 and 3. Here, the reason why the diameter of the connecting portion 4 is set smaller than the diameter of the body portions of the preform covers 2 and 3 is that a blowing needle is installed at this position and the blow needle is inserted into the parison during blow molding. In order to perform the operation smoothly.

  Next, a method of blow molding the molded body of FIG. 1 will be described. In order to blow-mold the molded body 1, as shown in FIG. 2A, a cylindrical parison 11 is extruded from a die of an extruder 12, and is sandwiched between a pair of split molds 13 and 14, as shown in FIG. 2B.

  As described above, the parison 11 is formed by extruding the melt-kneaded raw material resin from the die of the extruder 12, but any thermoplastic resin can be used as the raw material resin. For example, polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate, polyamide resins such as nylon, ethylene-vinyl alcohol resin excellent in gas barrier properties, and the like, but are not limited thereto. The resin may be appropriately selected from various resins according to the use of the preform covers 2 and 3 and the required performance and function. In addition, various additives such as a coloring agent, a light-shielding agent, an ultraviolet absorber, and a lubricant, a filler, and the like can be added to the raw material resin. Materials to be added may be appropriately selected according to performance, function, and the like.

  The split molds 13 and 14 have two cavities 13a and 14a respectively corresponding to the shapes of the preform covers 2 and 3, which are products, and the cavities 13a and 14a corresponding to the shapes of the preform covers 2 and 3, respectively. Protrusions 13b and 14b for forming the connection portion 4 having a slightly smaller diameter are formed between 14a. In addition, pinch-off portions 13c and 14c are provided at the ends of the cavities 13a and 14a on the side opposite to the side connected by the connection portion 4. When the split molds 13 and 14 abut against each other, the pinch-off portions 13c and 14c abut, and both ends of the parison 11 are crushed and closed.

  As shown in FIG. 2B, the mold is closed, the parison 11 is sandwiched between the pair of split molds 13 and 14, and the blowing needle 15 is inserted into the parison 11 at the protruding portion 13 b corresponding to the connecting portion 4, and the air blow is performed. I do. In the protrusion 13b corresponding to the connecting portion 4, the distance between the parison 11 and the split mold 13 is larger than the distance between the parison 11 and the split mold 13 in the cavities 13a and 14a corresponding to the shapes of the preform covers 2 and 3. It is small and can easily insert the blowing needle 15 into the parison 11.

  When blowing air, it is necessary to insert the blowing needle 15 in a state where the parison 11 is brought into close contact with the mold by vacuum suction. It is difficult to insert the blowing needle 15 into the parison 11 in a state where the parison 11 is attracted to the mold and is not in close contact with the mold, that is, in a state where the parison 11 is separated from the mold. Therefore, in order to quickly attract the parison 11 to the mold, it is advantageous that the distance between the parison 11 and the mold is small. By making the diameter of the connecting portion 4 smaller than the diameter of the body portions of the preform covers 2 and 3, the mold portion corresponding to the connecting portion 4 is projected more than the mold portion corresponding to the body portion. As a result, the mold part corresponding to the connecting portion 4 comes closer to the parison 11.

  The inner diameter of the mold portion corresponding to the connecting portion 4 is preferably substantially equal to the outer diameter of the extruded parison, and specifically, the inner diameter of the mold portion is 0 to 2 mm than the outer diameter of the parison. Is preferred. In order to reliably prevent the parison from being caught in the mold portion, the inner diameter of the portion is preferably larger than the outer diameter of the parison by 0.5 mm or more.

  In the present embodiment, the blowing needle 15 is installed on the protruding portion 13b which is a mold portion protruding corresponding to the connecting portion 4, and the blowing needle 15 is inserted into the parison 11 and air blow is performed. For example, a blowing needle 15 is provided on the protruding portion 13b, and a vacuum suction hole is provided around the blowing needle 15. When inserting the blowing needle 15 into the parison 11, vacuum suction is performed through these vacuum suction holes. By this vacuum suction, the parison 11 is attracted to the mold (projection 13b). Since the distance between the protrusion 13b and the parison 11 is short, the parison 11 is quickly attracted to the protrusion 13b and closely adheres. Therefore, the spraying needle 15 can be smoothly inserted into the parison 11.

  In addition to the case where a needle hole for letting a blowing needle protrude is provided in the protruding portion 13b which is a protruding mold portion corresponding to the connecting portion 4, a concave portion is locally provided in the protruding portion 13b and the concave portion is provided. May be provided, and a plurality of suction holes for sucking a parison may be arranged around the needle hole in the concave portion so as to surround the needle hole. For example, a circular portion having a diameter of about 4 to 6 mm and a concave portion having a depth of about 2 to 4 mm are provided on the protruding portion 13 b, a needle hole having a diameter of 2 to 3 mm is provided at the center of the concave portion, and a needle hole of 45 ° is formed around the needle hole. Eight suction holes may be arranged around the needle hole at intervals. In this case, when the periphery of the concave portion is close to the parison, when the parison is sucked by the suction hole in the concave portion, the parison partially enters the concave portion, and the parison can be firmly held in the portion where the parison has entered. Thereby, the blowing needle can be more reliably inserted into the parison.

  As shown in FIG. 2C, the parison 11 is pressed against the inner walls of the cavities 13a and 14a of the split molds 13 and 14 by the air blowing by the blowing needle 15, and is shaped into the cavities 13a and 14a. Next, the mold is opened and the molded body is taken out. The molded body to be molded is as shown in FIG. The removed molded body 1 is cut at the position indicated by the broken line in FIG. 1 and separated into individual products (preform covers 2 and 3).

  Next, the reason why the thickness of the product (preform covers 2 and 3) is made uniform when the blow molding method of the present embodiment is adopted will be described.

  FIG. 3A and FIG. 3B show the form of the parison 11 in blow molding in which a product is so-called one-piece. In the single-piece blow molding, one cavity 21a, 22a is formed in the split molds 21, 22 corresponding to one product, and pinch-off portions 21b, 22b are provided at both ends. .

  When one piece is taken, as shown in FIG. 3A, the pinch-off portions 21b and 22b are provided on both sides of the product (that is, the cavities 21a and 22a), and the distance L1 between the pinch-off portions 21b and 22b is small. In the pinch-off portions 21b and 22b, a large force is applied to the parison 11 at the time of cutting off, causing deformation of the parison 11, but when the distance L1 is small, the influence is exerted on the entire product.

  FIG. 3B shows a cross section of the parison 11 when the parison 11 is sandwiched between the split molds 21 and 22. The parison 11 is flattened by the influence of the pinch-off portions 21b and 22b provided on both sides of the cavities 21a and 22a. The phenomenon of collapse is seen. If the parison 11 is flattened, it will not be stretched uniformly when air blows, and the thickness variation in the circumferential direction will be particularly large.

  On the other hand, when the blow molding is performed by so-called two-piece molding as in the blow molding method of the embodiment, as shown in FIG. 4A, in the two cavities 13a and 14a provided on the side not connected to each other. The pinch-off portions 13c and 14c are provided only at the ends, that is, the ends opposite to the side where the protruding portions 13b and 14b for forming the connecting portion 4 are formed. Therefore, only the ends on both sides of two products which are far apart are pinched off (burr bite), and the connecting portion 4 is not pinched off.

  Here, the distance L2 between the pinch-off portions 13c and 14c at both ends is approximately twice as large as that in the case of the single-punching, and the influence of the cut-off at the pinch-off portions 13c and 14c is greatly reduced. As a result, as shown in FIG. 4B, the cross section of the parison 11 sandwiched between the split molds 13 and 14 becomes almost circular. If the parison 11 is circular, it is uniformly stretched in all directions during air blowing, and is formed with a uniform thickness.

  Products (preform covers 2 and 3) formed by the blow molding method of the present embodiment having such a mold design are excellent in uniformity of the thickness in the circumferential direction. It is possible to produce high quality composite containers.

  Hereinafter, a production example of the composite container will be described. In order to produce a composite container, first, a preform 40 made of a plastic material is prepared. Examples of the method of forming the preform 40 include injection molding using an injection molding machine, extrusion molding, and the like.

  The constituent material of the preform 40 may be any thermoplastic resin, and may be appropriately selected according to the use and performance of the composite container. Specific examples of the thermoplastic resin include PE (polyethylene), PP (polypropylene), PET (polyethylene terephthalate), and PEN (polyethylene naphthalate).

  Further, the preform 40 may have a multilayer structure. For example, a two-layer preform, gas barrier properties such as nylon MXD6 (trade name), nylon MXD6 (trade name) + fatty acid salt, PGA (polyglycolic acid), EVOH (ethylene vinyl alcohol copolymer), or PEN (polyethylene naphthalate) or light shielding It is also possible to prepare a preform comprising three or more layers having a resin having an intermediate property as an intermediate layer.

  Next, as shown in FIG. 5A, the preform cover 2 (3) is attached to the outside of the preform 40. The preform covers 2 and 3 have a cylindrical shape with a bottom as a whole, and have a cylindrical body and a bottom closed by pinch-off. As shown in FIG. 5B, the preform cover 2 (3) is mounted so as to cover the entire preform 40 except for the neck of the preform 40.

  After attaching the preform covers 2 and 3 to the preform 40, a heat treatment can be performed. For example, by performing a heat treatment at about 50 ° C. to 100 ° C., the preform covers 2 and 3 are thermally contracted, and the adhesion between the preform 40 and the preform covers 2 and 3 can be improved.

  Next, the preform 40 on which the preform covers 2 and 3 are mounted is preheated and set in a molding die. The preheating temperature may be set to an appropriate temperature according to the constituent material of the preform 40 and the like, and is, for example, about 90 ° C to 130 ° C.

  After the preheating, the preform 40 on which the preform covers 2 and 3 are mounted is set in a mold. The mold has a cavity corresponding to the shape of the composite container to be molded, and the preform 40 and the preform covers 2 and 3 are stretched by blowing air into the preform 40 softened by heating. Shaped into a cavity shape.

  Thereby, the composite container 50 is formed in which the outside of the container body 51 formed by stretching the preform 40 is covered with the coating layer 52 formed by stretching the preform covers 2 and 3. You. In the composite container 50 to be manufactured, since the preform covers 2 and 3 are formed by blow molding, the manufacturing cost can be reduced as compared with the case where the preform covers 2 and 3 are injection molded. it can. Although the preform covers 2 and 3 are formed by blow molding, the preform covers 2 and 3 have excellent uniformity in thickness as described above, and therefore, the coating layer 52 of the composite container 50 also has uniformity in thickness. It is excellent, and a high-quality composite container 50 can be formed.

  The embodiment to which the present invention is applied has been described above. However, it is needless to say that the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the gist of the present invention. It is possible.

  For example, in the above embodiment, two products are taken, but as mentioned above, three or more products can be taken. When three or more pieces are taken, the applicable form of the product is limited to one having both ends opened. For example, in the above-described preform cover, it can be used in a form that covers only the body of the container. It is. From the viewpoint of uniform thickness, the greater the number of products to be connected, the more advantageous.However, since the size of the mold is increased, the number of pieces to be taken depends on the product form and the required performance. It may be appropriately selected according to the size of the equipment and the like.

  In the above embodiment, the molding of the preform cover was described as an example, but the product is not limited to the preform cover. The present invention can be applied to the case where thickness uniformity is required in all blow molding.

EXAMPLE A preform cover having a cylindrical body, one end closed and multiple ends open was blow molded. The set thickness at the trunk of the molded preform cover is 0.5 mm.

  At the time of blow molding, as described in the previous embodiment, two preform covers were formed, and the two preform covers were collectively molded in a state where the two preform covers were connected via a connecting portion having a smaller diameter than the body. The connecting portion is not pinched off, and therefore only pinches off (burr bites) at the ends of the preform covers that are not connected to each other.

Comparative Example Similar to the example, a preform cover having a cylindrical body, one end closed and multiple ends open was blow molded. The set thickness at the trunk of the molded preform cover is 0.5 mm as in the example.

  The blow molding was performed by so-called single-piece molding. Therefore, the pinch-off (burr bite) is both the closed end and the open end of each product (preform cover).

The thickness distribution of the preform covers molded in the evaluation examples and the comparative examples was measured. The measurement location was set every 10 mm in the height direction. FIG. 6 is a diagram showing measurement points at which the thickness distribution of the product (preform cover) S was measured. In the figure, measurement was performed at seven points 1 to 5.

  FIG. 7 shows the thickness distribution in the longitudinal direction of the preform cover manufactured in the example. As is clear from FIG. 7, in the product (preform cover) manufactured in the example, the parting line position (PL-1, PL-2) and the position PL90 orthogonal to the parting line at each measurement point. The difference in thickness at -1 is 0.05 mm or less.

  In the range of two-thirds from the top (opening side) in the height of the preform, the variation in the thickness is preferably smaller than the average thickness (average of the two-thirds range = about 0.5 mm). , Plus or minus 10% (about 0.45 to 0.55 mm). The embodiment satisfies this condition.

  Similarly, the same measurement was performed on the preform cover (the preform cover blow-molded by pinching off both ends) manufactured in the comparative example. Exceeds 0.1 mm, and it was found that the above condition was not satisfied.

1 Molded product 2, 3 product (preform cover)
4 Connecting part 11 Parison 13, 14 Dividing mold 13a, 14a Cavity 13b, 14b Projecting part 13c, 14c Pinch-off part 15 Blowing needle

Claims (4)

In a blow molding method in which a parison extruded from an extruder is sandwiched between a pair of molds and blow molded,
The product to be molded is a preform cover that is molded by overlapping with the preform,
A blow molding, wherein the molded product is in a form in which a plurality of products are connected, and only the ends of the products at both ends that are not connected are pinched off to blow-mold the plurality of products at a time. Molding method.   2. The method according to claim 1, wherein the two products are connected at one end, and only the end of each product that is not connected is pinched off to blow-mold the two products at a time. Blow molding method.   3. The blow molding method according to claim 1, wherein a blowing needle is inserted into a portion to be connected, and air is blown.   4. The mold according to claim 3, wherein a mold part for forming a part to be connected is protruded, the parison is sucked and held by the protruding mold part, and a blowing needle is inserted into the held parison. Blow molding method.

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